ALD-assisted synthesis of V₂O₅ nanoislands on SnO₂ nanowires for improving NO₂ sensing performance

Anchoring nanoparticles on the surfaces of metal oxide nanosensors is a promising strategy to improve sensing performance. However, several issues regarding the surface coverage and uniform distribution of nanoislands over base sensing materials have yet to be resolved using conventional synthetic routes. Herein, we present a viable alternative for the decoration of V₂O₅ nanoislands on SnO₂ nanowires: a new two-step process that combines atomic layer deposition (ALD) and successive thermal post-treatment. This process enables us to control the surface coverage of V₂O₅ nanoislands by varying the number of ALD cycles and to homogeneously disperse the nanoislands on the SnO₂ nanowire surfaces. The NO₂ response of the V₂O₅-decorated SnO₂ sensor improved as the number of ALD-V₂O₅ cycles increased; the highest response, obtained by the sensor prepared with 50 ALD-V₂O₅ cycles, was more than 50 times greater than that of the pristine SnO₂ nanowires. However, the sensing performance degraded beyond 50 ALD-V₂O₅ cycles as there was an oversupply of V₂O₅ nanoislands. Based on density functional theory calculations, we determined that V₂O₅ nanoisland loading is in competition with the exposed SnO₂ surface to increase sensing performance, which implies that the surface coverage of V₂O₅ nanoislands must be precisely optimized.